Millwall boss Neil Harris has refused to comment on links with Blues keeper Bartosz Bialkowski and a number of other players.
Bialkowski, 31, is understood to be interesting the Lions, who are very much in the market for keepers with David Martin having joined West Ham, Ben Amos's loan from Bolton having ended and Jordan Archer having decided to move on this summer with his contract up.
In addition to their interest in Bialkowski, Millwall are believed to have had a bid turned down by Portsmouth for Jamal Lowe and are said to be eyeing QPR’s Matt Smith.
"We’ve been linked with players. Some are right and some come completely from nowhere, players from countries where we’ve never heard of the player,” Harris told London News Online.
"We have never recruited from abroad, so it’s not likely we will sign one from Outer Mongolia on a 12-year contract.
"Some will be true — that we have enquired about or made a bid for. Sometimes reports come out but we like to do our business in private and not alert other clubs to what we’re doing and what we’re spending.
"When it does come out it comes out from one place — and that’s an agent. I won’t be talking about individual players at other clubs.”
As well as Millwall, Birmingham City are among a number of clubs eyeing a move for Bialkowski, renewing their interest from last summer.
Town are understood to be willing to consider bids for the Polish international, who is the highest-paid player at Portman Road following the bumper new deal he signed last year after returning from duty with Poland at the World Cup finals in Russia.
That new contract followed the Blues' refusal of a £3 million offer from Birmingham for the former Notts County and Southampton man, who, following a tough season for both club and player, is likely to fetch significantly less this summer, £1.5 million having previously been reported to be Town's valuation.
League One football will do nothing to improve Bialkowski’s international prospects and despite having said he is happy at Town - and that he plans to live in Suffolk once he retires - a move back to the Championship is likely to appeal should a club - whether those already linked or another side - firm up their interest.